1. Field of the Invention
The present invention relates to a process for producing a fluorinated vinyl ether having an ester group which has the formula EQU CF.sub.2 .dbd.CFOCF.sub.2 (CF(CF.sub.3)OCF.sub.2).sub.n-1 (Rf).sub.m CO.sub.2 R
wherein n represents an integer of 1 to 5; m represents 0 or 1; RF represents a C.sub.1 -C.sub.10 bifunctional perfluoro group and R represents an alkyl group.
2. Description of the Prior Art
The fluorinated vinyl ethers are useful as monomers for producing fluorinated polymers. The fluorinated vinyl ethers obtained by the process of the invention can be used as comonomers for forming cure-sites in fluorinated polymers and as monomers for producing fluorinated polymers having special functions, and can be used in various fields.
The processes for producing the fluorinated vinyl ethers having an ester group are disclosed in Japanese Patent publication No. 22327/1970 and British Pat. No. 1,145,445.
The conventional processes include the reaction of perfluoro diacyl fluoride with hexafluoropropylene oxide to produce perfluoro [2-methyl-3-Oxa-alkane] diacyl fluorides. In the second step, the diacyl fluoride is esterified with an alcohol preferably with methanol to produce the diester. The diester is then either saponified with an anhydrous methanol solution of potassium, sodium or cesium hydroxide to give the di-metal salt, or converted by a reaction with water to the diacid which is then neutralized with an aqueous solution of one of the above hydroxides. Then, the di-metal salt is converted by a thermal decomposition, to the mono-metal salt and the resulting mono-metal salt is hydrolyzed to give the fluorinated vinyl ether carboxylic acid and then the product is converted by an esterification to give the fluorinated vinyl ether having an ester group.
In the conventional processes, many reaction steps are required and the yield in the thermal decomposition of the di-metal salt of perfluorodicarboxylic acid is remarkably low such as about 25%. In order to apply the conventional process in industrial scale, many difficult operations are required.
It has not been known to produce fluorinated vinyl ethers having an ester group in an industrial scale in high efficiency.
The inventors have studied to produce the fluorinated vinyl ethers having an ester group in high yield through a less complicated process.
As the result, the following important facts have been found.
The fluorinated compounds having ##STR1## group at one end and an ester group of --CO.sub.2 R at the other end could be thermally decomposed at relatively low temperature whereby ##STR2## group is surprisingly converted to the fluorinated vinyl ether group (CF.sub.2 .dbd.CFOCF.sub.2 --) without modifying the ester group, and the fluorinated vinyl ether having an ester group could be obtained in high yield.
It has hither to been known that when fluorocarbonyl group (--COF) or an ester group (--CO.sub.2 R) is treated with an alkali metal hydroxide, they are converted to an alkali metal salt of carboxylic acid (--COOM). So, when a fluorinated acid fluoride having an ester group (FOC--A--CO.sub.2 R wherein A represents bifunctional perfluoro group) is treated with an alkali metal hydroxide, it is converted to the di-metal salt (MOOC--A--COOM).
On the other hand, it has been found that when a fluorinated acid fluoride having an ester group (FOC--A--CO.sub.2 R wherein A represents bifunctional perfluoro group) is treated with an alkali metal carbonate, only --COF group is surprisingly converted to --COOM group without any affection to --CO.sub.2 R group.
It has been found that the acid fluoride having the formula EQU FOC(CF(CF.sub.3)OCF.sub.2).sub.n (Rf).sub.m CO.sub.2 R
could be converted to an alkali metal salt of fluorinated carboxylic acid having an ester group which has the formula EQU MOOC(CF(CF.sub.3)OCF.sub.2).sub.n (Rf).sub.m CO.sub.2 R
in high yield by the reaction with an alkali metal carbonate.
While the conventional process, which gives the fluorinated vinyl ethers having an ester group, required many reaction steps, pyrolyzing the alkali metal salts of fluorinated carboxylic acids having an ester group provides a more simpler way of production.